Sound-chamber and set-frame therefor



June 30, 1931. 1.. DE FOREST SOUND CHAMBER AND SET FRAME THEREFOR Filed Sept. 4, 1925 2 Sheets-Sheet lum/"tor L55 0155x557" June 30, 1931. DE FOREST 1,812,687

SOUND CHAMBER AND SET FRAME THEREFOR Filed Sept. 4, 1925 2 Sheets-Sheet 2 MW L55 05/5/2567 abhor/"w Patented June 30, 1931 UNITED STATES PATENT OFFICE LEE DE FOREST, NEW YORK, N. Y., ASSIGNOR TO DE FOREST PHONOFILM. COR- PORATION, OF NEW YORK, N. Y.,

SOUND-CHAMBER- AND Application filed September T his invention relates to sound-chambers and set-frames therefor for use in the electrical transmission of sounds originating in chambers provided with such frames, particularly in the making of sound-photographs and more particularly in making sound-andmotion photographs such as those photographed and projected by my phono-film s stem.

The most particular object of the invention is the construction of sound-chambers and of set-frames as elements thereof which will permit a good photographic record to be made on a motion-picture film of the sounds which accompany the motions or actions, both the sounds and the actions being recorded simultaneously on the film to constitute the sound-and-motion pictures; the object being to provide such a construction as will prevent such reflections of the sound as will cause an inferior sound photograph to be produced.

The invention consists of the sound-chamber, the set-frames therefor, and a certain important element of the set-frame, substantially as shown in the drawings, of which:

Fig. 1 is a view of a sound-and-motion picture set constructed of my novel setlrames so as to constitute a sound-chamber suitable therefor;

Fig. 2 is a rear elevation of one of the set-frames constituting the sound'chamber of Fig. 1;

Fig. 3 is a front elevation of such setframe;

Fig. 4 is a triple enlargement of the filling for the set-frame of Figs. 2 and 3; and

Fig. 5 is an enlarged detail illustrating the warp and filling strands of the fabric of Fig. 4.

The walls of sound-chambers or sets for motion pictures heretofore have consisted of a thick, hard, heavy composition board known as compo and substantially opaque to sound, that has been used in lieu of the portable canvas scenes used generally in the theatrical art. Such compo walls of motion-picture sets have various advantages in the motion-picture art over canvas scenes, and they have been quite satisfactory so long as only motion and not sound, 1s photo- A CORPORATION OF NEW YORK SET-FRAME THEREFOR 4, 1925. Serial N0. 54,397.

graphed; but when such compo boards are used in sets used for scenes in the photography not only of the action but also of the sounds made by the actors, it has been found that such boards cause sound reflections wiich seriously impair the quality of the sound-photographs, (that is, the sound record on the side of the motion-picture film, alongside the motion photograph thereon), the result being that complex sound waves are delivered to the microphone of the soundrecording apparatus, such waves being composed both of the waves direct from the initial source or origin of the sound inside the set and also of the wall-reflections thereof from the compo-board set back to the microphone inside the set. In short, the com 0- board set walls have acted as sound re ectors, just as do the walls of the building or permanent room themselves, in which the set usually is made up for the purpose of taking pictures. Thus, the compo-board set walls have not differed from the building or permanent room walls save asthey are temporary portable walls onwhich may be temporarily placed the desired scenes or attachments desired for a given motion picture in question.

Prior to the present invention no practicable means has been found, so far as I am aware, of providing set walls or any units thereof. which would prevent harmful sound reflections. Canvas, as employed for scenes in the general theatrical art, produces sound reflections, and the compo-board walls above mentioned have been preferred to canvas notwithstanding that the compo itself is a good sound reflector.

I have now discovered, however, a soundchamber composed of what I term setframes which not only completely overcomes the sound-reflecting difficulty abovedescribed, and permits the production of sound photographs which lack the defects resulting from reflection, but which possess certain additional advantages to be described.

In Fig. 1, PW indicates the walls of the building or room constituting the motionpicture studio, (if not outdoors) these walls sired or convenient. Practical use has being usually of great height, and the set being made up on any desired location of the floor and extending vertically only a fraction of the height of side walls PlV. The set shown in Fig. 1 within the side walls PV consists of a plurality of vertical setframes such as that shown in Figs. '2 and 3. These set-frames comprise a skeleton support K and a suitable front filling F to be described, and theseset-framesresemble, in general superficial dimensions, the usual portable canvas scenery of the theatrical'art, being usually of greater vertical than hori Zontal dimensions; and the walls of the set of Fig. 1 being composed of a plurality of such set-frames, located vertically and edgeto-edge as indicated in Fig. 1; the indivicual set-frames being readily portable, and having low weight on account of the filling construction to be described.

As shown in Fig. 2, the filling-fabric F laps around the skeleton support K, around the sides and preferably the backs of the side and end thereof, where it is secured to frame K in any desired way as by small tacks T. The skeleton back support or backing K, as shown in Fig. 2, may consist of wooden slats for combined economy and lightness, constituting a set frame which is readily portable. In the best form of my set-frame, the skeleton support is"strea1n-line in the sense that while mechanically strong yet it opposes to the sound waves origi ating within the set or .sound chamber constituted of my set-frames, a minimum amount of sound-refleeting surface of the elements of support K itself. 'It is in this sense that support K is of skeleton construction, as well as in the sense of permitting an air backing in rear of front filling F and between the slats to ,pElXDll, soun (1 transmission to the microphones M (Fig. 1) when they are located outside the sound-chamber or set instead of inside the set as heretofore.

As indicated in Fig. l, the sounn-cl r vet constituted of the new set-' x I located as close to permanent side wall PYV two feet or eighteen inches, as indicated byspace andthe set frames may be loeated as far from wall PW as be deshown that the nature of the new set frame is. such that under the above conditions of location, there will be no harmful sound reflection from wall Pil even altho sufficient of the sound volume from within the sound chamber passes outwardlythrough the set-f 1- are sufiiciently to operate the microphones M. This is in contrast with all previous soundcham her walls for sets in motion-pic'tu re photography, which either themselves have been efficiently sound reflecting-0r else have been so transparent 'to sound waves as to cause reflections "from the permanent walls PW back to the microphones inside the set. The

air space in back of front filling F and be tween the slats constituting skeleton frame K constitutes a portion of the total air space X in rear of the set frames and between front filling F and the permanent walls PlV; and in connection with the skelctonconstruction of backing framesK;the nature of front fillingF is of essential importance. In addition to various practical advantages tobe described, the material I employ for front filling F possesses the capacity of preventing sound reflections from its surface, by virtue of the cooperative functioning of solid portions of filling F and of certain perforations therethrough, the latter being in direct communication with the air space back of front filling'F, between the slats of skeleton frame K and general air space X within building walls 'llV and outside of the'set constituted by-the novel set-frames.

I have discovered that if filling F is constructed in special fashion, such as illus rated in Figs. 4 and 5, it will absolutely prevent harmful sound reflections from it, originating inside the set, wh'enmou'nted on skeleton frames K not too closely -ad- ,iacent to permanent (sound-reflecting) walls PWV. As shown in Fig. 4, the filling consists of a coarse, loosely woven fabric, the warp and filling of which consist l hecharacter of these coarse strands R and their surfaces is such as to absorb a large'proportion of the volume of the air-waves of sound reaching the fabric; but the difiiculty, and probable practical impossibility, of .absorloing the entire sound volume is compensated for by the provision of the holes H, which permit the free-passage, through fabric filling F, of such'volume of the sound as otherwise might result in reflections from the 'surfaceo'f filling fF, even altho composed of strands R if'no such holes llwere provided. Thus, as in F g. 1, a certain proportion of the sound volumemay penetrate through filling "Ffromthe interiorof the set,"to the space'X between the rear of the set andthe permanent walls Pil but the sound-absorbing properties of the interwoven strands Rare such as to reduce the; volume of sound passing through filling F so that'the same is insufficient to cause sound reflections from Walls PIV which can retraverse space X and come back through holes H (Fig. 4) to the interior of the set or to the microphones wherever they may be.

Fillin F, in being assembled with skcle ton back i, is drawn fairly taut over the front of the latter, but not to such degree of tautness as will distort fabric F and cause an undesirable proportionate area of strands R and holes H.

Specifically, I have discovered that a very effective construction of front filling F is one wherein each strand R is a double strand, consisting of two duplicate strands or small ropes R1 laid side by side and closely adjacent, as shown in Fig. 4, the holes H (Fig. 4) lying between such pairs of strands. In Fig. 4 the filling F is shown at about triple scale. Holes H, although plainly discernible when front filling F is held toward the light, yet are much smaller than sound-absorbing strands R, and preferably smaller than don ble-strand ropes R1. Each individual strand R1 preferably consists of a pair of yet smaller strands S, Fig 5; and each strand S preferably consists of a plurality of very fine fibers I, as shown in Fig. 5. oles H preferably are smaller than small strands S. In a very efiicient front filling F, the holes H of Fig. 4 are about 1/64 inch square; the complete double strands R1 of Fig. 4 are about to inch wide; and each individual small strand S of Fig. 5 is about inch. In closeup, front filling F resembles a mat with holes which appear rather large and circular; but I have found that a structure with such holes, (permitting the desired sound-transparency of the frabric-holes H in cooperation with the sound-absorbing properties of the fabric strands), is entirely satisfactory with respect to the motion-picture camera, in that the lens of the latter does not see through the filling F in such a set as Fig. 1n0twithstanding that holes H are of substantial size.

Preferably the minute fibres I of Fig. 5, comprising strands S, are short waste cotton not suitable for use in ordinary cotton fabrics, but well adapted in the construction disclosed to constitute strands R of sound-absorbing properties.

The results of the structure of Figs. 2 and 3, consisting of the combination of the skeleton frame K and the front filling F, are that a portion of the volume of the sounds origi- 5 nating within the sound-chamber or set is set and walls PW. Thus, the set-frames are partially opaque and partially transparent to sound waves, this result being obtained preferably by a single thickness of the Woven fabric F of the above-described construction, i. e., a weaving of rather coarse or thick strands in a rather loose weave sufficient to provide holes H of the desired size relative to strands R. lVhile this filling F is a fairly thick fabric, yet it is comparatively light, and when assembled with skeleton frames K, constitutes a structure which is so light as to be readily portable, even when the frames are several feet in horizontal dimension and several yards in vertical dimension.

The fabric preferably is woven of natural colored strands and superficially resembles in structure the well-known burlap employed in the manufacture of sacks or bags for potatoes .and the like; but holes H are much smaller than the ordinary holes in the burlap fabric, and preferably strands R and the fabric itself are thicker, and heavier per unit area. I have found that holes H must not be too large so as to permit too great a proportion of the volume of sound originating in the said chamber of Fig. 1, to pass through the individual unit set-frames to the outside of the set, i. e., to the space X between the set and the permanent walls PIV; .and that these holes H should not be so large as to cause filling F to be sound-transparent to a degree sufficient to set up injurious reflections from walls PvV. It is sufficient, as a practical matter, if holes H be sufficient in size to permit transmission through filling F of such volume of sound as, if prevented from such transmission, would cause reflections from filling F notwithstanding the sound-absorbing qualities of fabric-strands .R. I-Ioles H are suiliciently large for the useful soundtransmitting purpose when they are not so large as to be seen by the lens of the motion-picture camera. Another important advantage of filling F with holes H of the proper size for use in photography of sounds and moving objects simultaneously, and with the fabric strands R as above described, isthat such fabric-filling F is adapted to take scene-paint without serious impairment of the sound-absorbing property of strands R or the sound-transmitting property of holes H, all as described later. i In fact, this is such an important advantage that it is very useful even if walls PIV be padded against soundlCfiQCflOil therefrom.

lVhile the primary purpose of the setframes consisting of skeleton K and front filling F is to prevent sound reflection therefrom inside the set, yet I have discovered that the set frames as above described possess a further important advantage in connection with the use of the microphones M (Fig. 1) which electrically transmit, to the sound-photographing apparatus, the sounds originating inside such a set as that of Fig. 1. v:For..e.\.'.2,unple, heretofore, onaccount of the :use of the sound-opaque compo-board walls, it has been customary in producing tall'iingsmotion pictures to locate the microphone inside the set, where, of course, it is practically necessary to camouflage the soundreceiving microphone in respect of the lens of the motion-picture camera. In the employment of the new set-frames for the pur pose of preventing sound reflections confusing the microphones, I have discovered that holes H (Fig. &) permit a sufficient soundtransparency of the set-frames to operate the microphones when the latter are located, as shown in Fig. 1, in back of the set frames and outside the sound-chamber, in the low-volume sound-zone X between the filling F and the permanent sound-reflecting walls PW. This is a very important advantage in practical sound-and-motion picture photography in that itpermits aplurality of microphones to belocated in various positions outside of but adjacent to the set, so that the ordinary motion-pict-ure problems are not interfered with by the necessity .of camouflaging, inside the set, a plurality of microphones so located as to receive sounds from the actors in their various locations inside the set at different angular relations to the walls thereof. Obviously, the difficulties involved in camoufla ging a single, microphone inside the set are very greatly complicated by the provision of a plurality of microphones. The set of Fig. 1, when composed of set-frames as described, in effect constitutes a high-volume inner soundchamber surrounded by a low-volume outside air-zone X between theoutside of the set and the permanent sound-reflecting walls PW; this being so whether or not permanent building-walls PW are padded against sound-reflection. lVith the set-frames hereof it is prac ticable to "have the sound volume in zone so smal las not to cause reflections from walls PlV (even if unpadded) which affect even the microphones M located in zone X, and at the same time to have that volume sufficiently large to operate microphones M satisfactorily via holes H in filling F) to cause the production of sound photographs on the motionpicture film. It will be understood, however, that the desired sounds reaching the micro phones can beamplified to any desired extent vbythe audion amplifying tubes employed in thesound-photography apparatus; and it is not to be understood that absolutely all sound reflectionsfrom walls PW are prevented by any and all forms and locations of the setframes hereof. Practical use of such setfframes, ghowevenhas demonstrated not only that any minor'reflections from walls PW will not injur-iously affect the microphones if located inside the'set, but will not do so even if the microphones be located. in the zone X-as shown in Fig. 1.

WVhen the set-frames hereof are provided with a filling-fabricF, substantially as herein described, the filling'F can be washed by water or the like as for cleansing, without shrinkage,, and while secured to and on skeleton K so as not to tear itself away from its ecuring meanssuch as tacks T; and such cleansing can be effected without injuriously affecting the construction of filling F which permits it to be partially sound opaque and partially sound-transparentas above described.

The fact is emphasized in Fig. 1 that the set-frames hereof have nothing striking or characteristic abouttheir appearance inside the set. The only portion of the set-frames which is visible inside the set is the front filling F (Fig. 3) and that in a natural color of strands as preferably woven has a natural neutral color which is suitable to represent in the set the walls of a room, for example. But filling F may be decorated or painted as described hereinafter. I

For cases where it is not convenient to obtain a special weave of fabric-filling F as above for mounting on the skeleton backs K, I have found ordinary coarse fabric known as monks cloth to be highly desirable .as the front filling sound-absorbing element of theset-frames, the same being a material frequently purchased by housewives in its natural neutral color as it comes from the loom and by-them dyed and cut as window draperies. Such cloth as a standard article of commerce I hrve found to possess to a very high degree the properties abovegset forth as suitable for this element of the set-frames hereof, because it usually has .a construction substantially the same as that shown in Figs. 4 and 5.

Skele ton'back K-may becomposed of other material. than wood, such for example as a lightwe ght metal as aluminum, but wood is qu te satisfactory (.altho of course inflam mable) and is adapted as a wall support for pictures and the like constituting parts of a complete set. In fact, in the matter of afiixing parts of the set to the set-frames hereof when'representing side walls as in theset of Fig. 1, the present invention is superior to the compo boards heretofore employed in motion-picture photography in the following respects. For example, if it be desired to hang a picture on the wall,as at P, Fig. 1, or to put up a wall shelf, as at L,.Fig. 1,

etc, all that is necessary, if the location'is not at aportion of wooden skeleton K already existing, is to nail to already-existing wooden slats of skeleton backing Kone or more additional slats,- as atKl, K2, Fig. 1, in which the nail or nails forthe picture, shelf or the like may be driven; and suchadditional skeleton parts as K1, IE, will not substantially affect the characteristic skeleton constructionof support K, andit need not injure the filling F, especially as holes H, Fig. 4, are sufficiently large to receive the points and then the shanks of small nails. Furthermore, when the front filling F has substantially the constituency above described, I have found that upon it, in position on skeleton K, it is practicable to paint desired decorations or scenes on its front face which, provided that the paint is not too thickly applied, will not substantially impair its soundreflecting property. Apparently such light paint coatings do not impair the sound-absorbing qualities of the coarse strands R and do not so block up holes H as to interfere with sound transmission therethrough. Also, not only can the filling F be washed for ordinary cleansing, but the thin coat of scenepaint itself can be removed while filling F remeans secured to the skeleton K, by any desired paint removers, without injury to the fabric, thereby permitting the entire setframe to be used repeatedly in various different sets. Even without painting filling F by direct application of a brush, it may be stippled in color so that the joint effect of its natural neutral state and the stippling in color provides a very desirable appearance as a representation of room walls.

The set-frames hereof are light in weight for size, which is a most important desideratum in motion-picture studio work where the sets are composed of portable units which are carried about and set in place and taken down and stored and handled generally, all by manual labor.

The temporary room or sound-chamber of Fig. 1, composed of two or more side walls, may or may not have a ceiling composed of the set frames hereof, depending upon whether the space in which the set is made up is provided with a low permanent sound-reflecting ceiling. Usually the structures or studios in which sets are made up either have such high ceilings or roof as to cause sound reflection thereof to be negligible in its effect upon the microphones, or else they have no ceilings or roof at all and consists only of a permanent platform, so that usually the set-frames hereof are not needed as ceiling elements.

When the studio is an open-air one and has no permanent part save a platform, with out side walls, the sound reflections heretofore in such cases have been caused by the thick and heavy compo boards constituting the walls of the set; and the set-frames hereof, even in the absence of any permanent sound-reflecting walls PW (Fig. 1) provide against harmful sound reflections.

In no case have I found that the sound reflection from carpeted floors has any injurious effect on the microphones, for with walls of sets composed by my set-frames and with the usual high ceilings or roofs of the studio buildings, all injurious sound-reflecting action has been eliminated. Preferably the floor, Fig. 1, is to be carpeted or more or less covered with rugs.

The set-frames and sound-chambers hereof have been tested out fully under actual operating conditions in my own talkingmotion picture studio and have been proved. to possess all the desirable properties above described.

In Fig. 1 is shown an example of a permissible modification of the set frames to provide for representations of windows or doors, as shown at the door D, which is: shown as partly open, disclosing another microphone M arranged in the low-volume sound-zone X outside of the set. Door D itself may consist of a suitably shaped unit of the set-frame hereof provided with its own separate skeleton bacl-z K and the set-frame above door D can be supported by having its wooden slats of skeleton K nailed to the wooden slats of the adjacent set-frames arranged edge-on to it at the opposite edges thereof. This illustrates the fact that the set-frames hereof are valuable in their simplicity and the ease with which desired lengths of filling F can be cut and applied to a skeleton K readily constructed for special occasions out of the nailed-together wooden slats.

t is to be noted that the property of the set-frames hereof in preventing injurious sound reflections from either their own surfaces or from the permanent sound-reflecting walls PIV (Fig. 1) outside the set (when such permanent walls exist) is due to the fact that a certain proportion of volume of sounds originating inside the set is permitted to pass freely through holes H (Fig, 4) of front filling F through the air spaces between the slats of skeleton backing K, and to the fact that substantially all the remainder of the volume of sounds originating inside the set is caused to be absorbed by the material F of the filling itself, the minute fibres I (Fig. 5)

of individual strands S being so closely woven into such individual strands as to constitute substantial sound-opacity; so that the properties of set-frames KF of partial soundopacity and partial sound-transparency act jointly in preventing the injurious sound reflections. This is true whether or not the frame-filling F be scone-painted.

Inasmuch as the screens of this invention absorb part of the sound and allow part of the sound to pass through they may be called sound-translucent although there is no distortion of the sound but-only partial absorption.

I particularly point out and distinctly claim the part, improvement or combination which I claim as my invention or discovery as follows:

1. A sound-permeable motion picture background for use in the simultaneous photography of sound and motion, consisting of liIO sidewalls which include a, skeleton support and a filling of a sheet of coarse-Weave, openmesh cloth mounted on saidsupport, the holes in said cloth being in free communication with substantial air-spaces inside andoutside the background; and an electrical soundtransmitter associated with said background and hidden thereby.

2. A temporary sound-originating motion picture set for supplying sound-Waves to an electrical sound-transmitter, said set being formed by side-Walls including a basket- Weave cloth in a plurality of sheets located edge to edge and independently mounted on light portable skeleton frames.

3. A non-sound-refiecting portable set frame including a light skeleton support and a front filling thereon consisting of'a light thin sheet of non-sound reflecting material formed with sound-transmitting holes, the

relative proportion of such holes and material and the character of the material permitting transmission, Without undesirable reflection, of sounds originating on the front side of the sheet to an electrical sound transmitter located'on either side thereof.

4; A portable sound-permeable set-frame which comprises a skeleton support having mounted thereon a light-porous sheet of nonsound-reflecting material.

5; A scenery set comprising a frame covered With non-sound-reflecting, soundtransmitting, porous fabric which is photogralphically opaque and provided With a I decoration-receptive face.

LEE DE FOREST. 

